1. Field of the Invention
The present invention relates to a battery pack and a battery system using this battery pack.
2. Description of the Related Art
The present applicant has previously proposed a charging device which is, upon charging a battery pack, capable of indicating a drive possible time of an electronic device using a battery cell being charged and its current charging capacity as shown in FIGS. 1 to 4.
This charging device will be described. In FIG. 1, reference numeral 1 denotes a charging device housed in an electronic device such as a video tape recorder having a built-in camera (hereinafter referred to as a video camera) or the like. Also, in FIG. 1, reference numeral 2 denotes an AC adapter 2 connected to a commercially-available power supply to supply the power to the video camera and the charging device 1.
This charging device 1 includes a charging circuit 3, a calculation processing microcomputer 5 and a display device 6 and this charging circuit 3 charges a battery cell 20 (see FIG. 2) of a battery pack 4 that is used to drive the video camera when a user carries the video camera. The charging circuit 3 is arranged as is well known in the prior art. This battery pack 4 includes at least a battery calculation processing means 4a for obtaining battery cell voltage detection information and charging current cumulated amount information and an a communication processing means 4b for communicating each of the information.
An example of this battery pack 4 is shown in FIG. 2. Referring to FIG. 2, a positive electrode of the battery cell 20 of the battery pack 4 is connected to a plus terminal TM1 of this battery pack 4, and a negative electrode of the battery cell 20 is connected through a current detection resistor R7 to a minus terminal TM2 of this battery pack 4. The plus terminal TM1 and the minus terminal TM2 are respectively connected to a plus terminal and a minus terminal at the output side of the charging circuit 3 of the charging device 1.
The power from a microcomputer power supply 16 including a series regulator, a reset circuit or the like is supplied to a microcomputer 10 housed in the battery pack 4. The microcomputer 10 is operated by the power supplied from this microcomputer power supply 16. By the way, the microcomputer 10 has functions of the battery calculation processing means 4a and communication processing means 4b. A charging current detection input terminal D11 of this microcomputer 10 is connected to an output terminal of an operational amplifier 13 provided to detect a charging current. A discharging current detection input terminal D12 thereof is connected to an output terminal of an operational amplifier 14 provided to detect a discharging current. Both the operational amplifiers 13 and 14 detect charging and discharging currents based on the voltage difference across the current detecting resistor 7.
An interrupt input terminal of the microcomputer 10 is connected to an output terminal of a 2-input NAND gate 15 having two input terminals connected to the respective output terminals of the operational amplifiers 13 and 14. Further, the output terminal of the 2-input NAND gate 15 is connected through a pull-up resistor R8, for example, to a power supply terminal. Also, a temperature detection input terminal of the microcomputer 10 is connected to an output terminal of a temperature sensor 19 which detects an ambient temperature of the battery cell 20. A voltage detection input terminal thereof is connected to an output terminal of a voltage detection circuit 18 which is used to detect a terminal voltage of the battery cell 20. A ground terminal GND thereof is connected to the negative electrode of the battery cell 20. An output and input terminal TMC used to communicate with the calculation processing microcomputer 5, which comprises a computation means of the charging device 1 of the video camera as will be described later on, is connected to buffer amplifiers 11 and 12.
Incidentally, analog input terminals such as the charging current detection input terminal D11, the discharging current detection input terminal D12, the temperature detection input terminal, the voltage detection input terminal and so on are all A/D input ports. Therefore, the microcomputer 10 houses an A/D converter for converting these analog input into digital form.
The voltage detection circuit 18 is formed of a voltage-dividing resistor comprising resistors R9 and R10. A voltage across the battery cell 20 is detected by this voltage-dividing resistor. A voltage detection value from this voltage detection circuit 18 is supplied to the voltage detection input terminal of the microcomputer 10. Accordingly, the microcomputer 10 is able to learn the terminal voltage across the battery cell 20 based on the voltage detection value supplied to this voltage detection input terminal from the voltage detection circuit 18.
Also, the temperature sensor 19 is comprised of a suitable device such as a temperature detection thermistor or the like. The temperature sensor 19 is disposed in the vicinity of or in contact with the battery cell 20, and a temperature detection value of this temperature sensor 19 is supplied to the temperature detection input terminal of the microcomputer 10. Accordingly, the microcomputer 10 is able to learn a temperature of the battery cell 20 based on the temperature detection value supplied to this temperature detection input terminal.
Then, a non-inverting input terminal of the operational amplifier 13 is connected through a resistor R3 to the negative electrode of the battery cell 20, and an inverting input terminal thereof is connected through a current voltage detection resister R7 to the negative electrode of the battery cell 20 and also to an amplification factor setting negative feedback resistor R2 and a resistor R1. Accordingly, the operational amplifier 13 outputs from its output terminal a voltage value which results from amplifying a current value (current value flowing upon charging) flowing into the battery pack 4 in response to a ratio (R2/R1) of resistance values of the resistors R1 and R2.
On the other hand, a non-inverting input terminal of the operational amplifier 14 is connected through a resistor R6 and the current voltage detection resistor R7 to the negative electrode of the battery cell 20. An inverting input terminal thereof is connected to a negative feedback resistor R5 and a resistor R4. Accordingly, the operational amplifier 14 outputs from its output terminal a voltage value which results from amplifying a current value (current value flowing upon discharging) flowing into the battery pack 4 in response to a ratio (R5/R4) of resistance values of the resistors R4 and R5.
A transistor switch Tr1 is comprised of a field-effect transistor, for example, and whose gate is connected to a switching control output terminal SW1 of the microcomputer 10. The resistor R1 is connected between the drain and the source of this transistor switch Tr1. Accordingly, when the level of the signal from the switching control output terminal SW1 of the microcomputer 10 goes to a high (H) level, for example, the transistor switch Tr1 is turned ON, whereby the resistance value based on this resistor R1 becomes approximately 0 (there is only the internal resistor of the transistor switch Tr1), thereby resulting in the amplification factor (amplifier gain) of the operational amplifier 13 whose amplification factor is set in response to the ratio (R2/R1) of the resistance values of the resistors R1 and R2 being increased.
On the other hand, when the level of the signal from the switching control output terminal SW1 of the microcomputer 10 goes to a low (L) level, for example, the transistor switch Tr1 is turned OFF, whereby the amplification factor of this operational amplifier 13 becomes such one corresponding to the ratio (R2/R1) of the resistance values of the resistors R1 and R2, i.e. amplification factor (amplifier gain) smaller than that obtained when the transistor switch Tr1 is placed in the ON state. Similarly, a transistor switch Tr2 is comprised of a field-effect transistor, for example, and whose gate is connected to a switching control output terminal SW2 of the microcomputer 10. The resistor R4 is connected between the drain and the source of the transistor switch Tr2.
Accordingly, when the level of the signal from the switching control output terminal SW2 of the microcomputer 10 goes to a high (H) level, for example, the transistor switch Tr2 is turned ON, thereby resulting in a resistance value of the resistor R4 being decreased to approximately 0 (there is only the internal resistance of the transistor switch Tr2). Thus, the amplification factor (amplifier gain)of the operational amplifier 14 increases. On the other hand, when the level of the signal from the switching control output terminal SW2 of the microcomputer 10 goes to a low (L) level, for example, the transistor switch Tr2 is turned OFF, thereby resulting in the amplification factor (amplifier gain)of the operational amplifier 14 being decreased.
The microcomputer 10 constantly monitors the levels of the charging current detection input terminal D11 and the discharging current detection input terminal D12 in the normal operation mode (Run mode). When the levels of these terminals D11, D12 are higher than the constant level, the microcomputer 10 causes the signal levels of the switching control output terminals SW1 and SW2 to be held at low level. Thus, the transistor switches Tr1 and Tr2 are both turned OFF, thereby resulting in the amplifier gains of the operational amplifiers 13 and 14 being decreased. Therefore, the microcomputer 10 in the normal operation mode (Run mode) becomes able to measure a current value (current value flowing in the charging or current value flowing in the discharging) flowing into the battery pack 4 by using the output values obtained from the operational amplifiers 13 and 14 whose amplifier gains are decreased. Accordingly, if the current values in the charging and the discharging are obtained, then it becomes possible to calculate the charging and discharging current cumulated value.
Also, in the above-mentioned example, data of a battery cell voltage V, a charging current I, a charging current cumulated amount Q and temperature dependence coefficients h1(T) and h2(T) from the battery pack 4 are supplied to the calculation processing microcomputer 5 comprising the computing means of this charging device 1.
Also, data of a power consumption W of a video camera using this battery pack 4 is supplied to this calculation processing microcomputer 5.
This calculation processing microcomputer 5 is operated in accordance with a flowchart shown in FIG. 4. This calculation processing microcomputer 5 computes the charging capacity of the battery cell 20 of the charged battery pack 4 being charged and displays a computed charging capacity on the display device 6 which will be described later on. At that same time, this calculation processing microcomputer 5 computes a time during which the present charging capacity can run the video camera using this battery pack 4, and displays this computed time on the display device 6.
[0020]
This display device 6 includes a present charging capacity indicator 30 comprising 5-step indicators a, b, c, d, e as shown in FIG. 3. The uppermost portion in the indicator upon charging is blinked. When the charging capacity ranges from 0 to 20%, for example, the indicator a is blinked; when the charging capacity ranges from 20 to 40%, the indicator a is lit and at the same time, the indicator b is blinked; when the charging capacity ranges from 40 to 60%, the indicators a and b are lit and at the same time, the indicator c is blinked; when the charging capacity ranges from 60 to 80%, the indicators a, b, c are lit and at the same time, the indicator d is blinked; when the charging capacity ranges from 80 to 100%, the indicators a, b, c, d are lit and at the same time, the indicator e is blinked; and when the charging capacity is greater than 100%, the indicators a, b, c, d, e are all lit.
Also, in the present charging capacity of the display device 6, as a running possible time indicator 31 of a video camera using this battery pack 4 that is being charged, there may be used numerals, e.g. time indication such as 229 min shown in FIG. 3.
An example of the manner in which the battery cell 20 of the battery pack 4 is charged by the charging device 1 according to the above-mentioned example will be described next with reference to a flowchart of FIG. 4.
Initially, the charging device 1 of the video camera is powered by the AC adapter 2, and the battery pack 4 which will be charged is attached to the video camera at its predetermined position. At that time, it is determined by the calculation processing microcomputer 5 whether or not the attached battery pack is a battery pack that can be charged (step S1). If the battery pack is a battery pack such as a dry cell or the like that cannot be charged, then the charging is ended.
If the attached battery pack 4 is the battery pack that can be charged, then the charging current is supplied from the charging circuit 3 of the charging device 1 to the battery cell 20 of the battery pack 4, and control goes to a step S2. In this step S2, the calculation processing microcomputer 5 in the charging device 1 receives data of a battery cell voltage V, data of a charging current I, data of a charging current cumulated amount Q and data of temperature dependence coefficients h1(T), h2(T) transmitted from the battery pack 4. Data of video camera power consumption data W also is stored in a memory provided in this calculation processing microcomputer 5.
Then, control goes to a step S3, and in this step S3, there are computed a charging capacity and a shooting possible time based on a present charging capacity.
This charging capacity can be obtained by a ratio of a charging current cumulated remaining amount S, obtained by the following equation, and a whole capacity of the battery cell 20. Incidentally, the whole capacity and temperature dependence coefficients h1(T), h2(T) are transmitted from the battery pack 4 through its communication processing means 4b.
Charging current cumulated remaining amount EQU S=(Q-g(W)).times.h2(T)
where g(W) is the discharge cumulated amount cumulated from the video camera running possible minimum voltage to the full discharge of the battery cell 20 and depends upon the power consumption W.
In this case, when the temperature dependence is not taken into consideration, this charging current cumulated remaining amount S is expressed as: EQU S=Q-g(W)
Charging capacity=S/whole capacity of battery cell
A video camera running possible time based on the present charging capacity of the battery cell during the charging can be obtained by multiplying the charging current cumulated remaining amount S with f(W) and the temperature coefficient h1(T) as expressed by the following equation. That is, the video camera running possible time R=S.times.f(W).times.h(T) where f(W) is the coefficient for converting the charging current cumulated amount Q into the video camera running possible time and which depends upon the power consumption W of this video camera.
In this case, if the temperature dependence is not taken into consideration, this video camera running possible time R is expressed as: EQU R=S.times.f(W)
Then, it is determined whether or not the charging capacity and the video camera running possible time thus calculated can be indicated (step S4). If they can be indicated, then the charging capacity and the video camera running possible time are displayed on the display device 6 of the charging device 1 as the indicators 30 and 31. The above-mentioned processing is repeated until the charging is ended.
According to the above-mentioned example, since the present charging capacity of the battery cell 20 being charged is calculated by the calculation processing microcomputer 5 of the charging device 1 and indicated on the display device 6 and the video camera running possible time of the video camera using this battery pack 4 is calculated based on the present charging capacity and indicated on the display device 6, the present charging capacity of the battery cell 20 being charged may be learned with ease, and the video camera running possible time of the video camera using the battery pack 4 may be learned with ease, thereby making the battery system become more convenient for the user.
However, in the above-mentioned charging device, when this charging device is formed independently of the electronic device such as the video camera or the like, it is necessary for the charging device to learn the power consumption of the electronic device that is driven by the battery pack 4. In order for the charging device to learn the power consumption of this electronic device, heretofore, there may be considered a method in which a signal line is used to connect this charging device and the electronic device to thereby input the power consumption of this electronic device into the charging device.
On the other hand, in the case of the electronic device such as the video camera or the like, in most cases or the like, the battery pack (discharging state) 4 which drives this electronic device and the charging device which charges this battery pack 4 are formed in many case independently of each other in order to maintain a safety or the like.
If this electronic device and the charging device are integrally formed as one body as seen in the above-mentioned example, then this charging device is difficult to have a highly value-added function such as boosting charge and custom charge for individual battery pack because a cost of a product increases and a space for mounting such charging device is limited.
Under such situation, if the electronic device and the charging device are made separately and the charging device is formed independently. in general, there are following requirements:
(1) To indicate a running possible time of an electronic device to which the battery pack is attach when the battery cell of the battery pack is charged by the charging device. Further, to correct an error of the electronic device running possible time indication in response to a future change of a power consumption of an electronic device driven by this battery pack. PA1 (2) To correct an error of a running possible time indication during an electronic device is in use by the electronic device driven to which this battery pack is attached after the electronic device has understood the degree in which the performance of the battery pack is lowered upon charging by the single charging device. PA1 (3) To correct an amount of a dark current flowing in the battery cell within the battery pack by the charging device or the electronic device driven by the battery pack during a time period from the end of the charging to the start of the discharging, from the end of the discharging to the start of the charging or the like.
When the charging device or the electronic device to which the battery pack is attached and driver thereby intends to meet with the above-mentioned requirements under the condition that the charging device and the electronic device are formed separately, the charging device needs to learn the situation (information) caused in the electronic device and the electronic device needs to learn the situation (information) caused in the charging device.
Heretofore, as a method of learning such situation (information) by the above-mentioned device, there may be considered a method in which this charging device and this electronic device are connected via a signal line and the situation (information) is interchanged and made common between the charging device and the electronic device.
However, according to this method, the signal line for connecting the electronic device and the charging device should be prepared additionally. At the same time, when this signal line is connected, it is unavoidable that a convenience, a portability and so on are deteriorated.